1. Field of the Invention
This invention relates to an optical recorder and a recording method used in a process of photolithography in producing a semiconductor integrated circuit, a liquid crystal display and the like, and more particularly, to an optical recorder and a recording method suitable for forming an exposure pattern and the like having a line width substantially as large as the wavelength of an exposure light.
2. Description of Related Art
Among optical recorders utilizing exposure, there is an exposure device for imaging an exposure pattern on a surface of an exposed object by a projection optical system such as a lens projection or a mirror projection. However, in case a line width of an exposure pattern is close to the wavelength of an exposure light, the line width was not resolved because of a limitation due to a diffraction of light. In order to settle this problem, there is provided a method which makes the resolution better by using as an exposure mask a phase-shift mask with a transparent or translucent phase-modulated layer called shifter formed on a mask base to modulate the phase of light in the phase-modulated layer, thereby to better the resolution.
There is another exposure device, i.e., a laser picturing device, which exposes an exposed object while continuously or intermittently scanning on the surface of the exposed object with a laser beam according to an exposure pattern to be recorded. Further, there is a laser picturing device which uses a spatial light modulator for modulating the amplitude of a light to image an exposure pattern formed in the spatial light modulator on an exposed object. This can simultaneously record an exposure pattern at a plurality of positions by the spatial light modulator for amplitude modulation, so that it is advantageous for realizing speeding up of picturing in comparison with a case of scanning with a single beam.
However, in a phase-shift mask, it is necessary to form a phase-modulated layer with a highly accurate thickness on a mask base, and in case the phase-modulated layer and an amplitude-modulated layer of a patterned chrome film or the like are combined, it is necessary to overlap the phase-modulated layer and the amplitude-modulated layer with high accuracy, so that it is more difficult to manufacture the phase-shift mast than an ordinary exposure mask and caused an increase in a manufacturing cost. Further, it was necessary to manufacture a phase-shift mask for each pattern.
Also, the laser picturing device using a spatial light modulator for amplitude modulation can draw a picture, but was inferior with respect to resolution to a device using a phase-shift mask.